Oscillation generator



Dec. 3, 1935. B. J. 'rHoMPsoN 2,022,988

OSCILLATION GENERATOR Filed April 29, 1933 2 Sheets-Sheet l INVENToR EPO/V275? 7, 7290/1712504/ ATTORNEY Dec. 3,` 1935.

B J. -\"H0MPSON USC'ILLAIION GENERATOR Filed April 29, 1935 2 Sheets-Sheet 2 Iillllllllllgllil ATTORNEY Patented Dec. 3,` 1935 UNITED STATES PATENT ori-'ice l 2,022,988 osCILLA'noN GENERATOR Browaer J. Thompson, East o c, N. J., as-

poration of Delaware Application Apru ze, 1933, serial Nasssszz 9 claims. (ci. asc-' es) My invention relates to oscillation generators of the thermionic vacuum tube type, and more particularly to an improved high frequency generator of this type capable of generating relatively l strong electric waves of a length less than one meter, and also to an improved .thermionic tube suitable for u'se in the generation of high frequency oscillations and for other purposes.

The lower'limit 'on the length of the electric waves produced by an electron discharge type of oscillation generator with regenerative coupling isreachedwhen the duration of travel of the electrons in the tube during each cycle of the generated frequency becomes appreciable in comparlson with the duration of the cycle, whereupon the conditions suitable for regenerative coupling are no longer present so far as the phase relation of the grid and anode alternating potentials are concerned. With the vacuum tubes now in general commercial use, the shortest waves that can be obtained with regenerative coupling have a length of approximately one meter, and are so weak that they are useful only for measuring purposes. Waves shorter than one meter can be produced with a three electrode vacuum tube by the Barkhausen and Kurz method, by applying a negative potential of about l0 to 20 volts to the plate electrode, and a positive potential of a few hundred volts to the grid which then becomes the anode.

According to Barkhausen and Kurz the high velocity electrons pass through the meshes of the highly positive grid electrode, stop and turn back in the retarding eld of the negative plate electrode, go back through the grid towards the cathode, stop in the retarding field of the cathode,

and turn back toward the grid. The electrons,

therefore, cscillate about or swing back and forth through the grid producing high frequency oscillations which will appear in an oscillating circuit connected tothe grid and the plate electrode. The frequency of these oscillations is determined by the time of travel of the electrons through the inter-electrode space and consequently depends upon the electrode spacing and the applied potentials.

Ielectrode when'- it is used as an Gill and Morrell have found that the same ar ent solely on electrode spacing and applied potentials, andthe other also dependent on the tuning of an oscillating circuit, may beproduced independently or even simultaneously by the same tube by adjusting the associated circuits. 5

The only type of tube which, so far as applicant is aware, has heretofore been successfully used as above described to generate ultra high frequency oscillations is the cylindrical type with the electrodes coaxial with a'straight cathode. Shorter 10 waves can be obtained by increasing the potentials or reducing the electrode spacing, but the extent to which the electrode spacing in the cylindrical type of tube can be reduced by decreasing the diameter of the electrodes is limited rather denitely by various difliculties, such as objectionable overheating of a small diameter grid anode at high potential, so that in general the usefulness and utility of such a tube tends to decrease as the diameter of the electrodes is reduced.- In this respect a fiat type of tube with at electrodes and a fiat cathode, such asa V or M shaped lamentary cathode of the usual type and dimensions and with its strands in a plane parallel to the other electrodes, wouldl theoretically have some advantages, but heretofore the production of ultra high frequency oscillations and ultra short waves with a tube having the usual V or M filament cathode and particularly with a at type of tube, has been considered impossible.

One object of my invention is to provide an improved oscillation generator of the thermionio vacuum tube type of a relativelyV high output and capable of generating oscillations, particularly ultra high frequency oscillations for producing the electric waves shorter than one meter which are commonly referred to .as ultra short waves. Another object is to provide a thermionic vacuum tube of the fiat type' particularly suitable for use as an uitrahigh frequency generator, and' also useful for other purposes.

:The'novel features which I believe to be characteristic of my invention are set forth with par 45 ticularity in the appended claims. My invention itself, however, will best be understood by reference to the following specification taken in connection with the accompanying drawings, in which Fig. 1 is a perspective view, with paris 5o broken away, of the mount of a fiat type of tube embodying my invention; Fig.v 2 is a horizontal cross section of Fig. 1 on the line 2-2; Fig.

a'perspective view, with parts broken away, of another modified form of tube; Fig. 5 is a horizontal cross section of Fig. 4 on the line 5 5; Fig. 6 is a diagram of a circuit for using a 'tube embodying my invention as an ultra high frequency generator; Fig. 7 is a diagram of a circuit for using the tube as a modulator; and Fig. 8 is a diagram of a circuit `for the tube shown in Fig. 4.

In the particular embodiment of my invention shown in Fig. 1 the electrodes of the tube are enclosed in a highly evacuated bulb not shown in the drawings, but indicated by the circles in Figs. 6 to 8. The electrodes are mounted on the usual stem I5 sealed into the bulb and having a plurality of projecting electrode supports I6 connected to leading-in wires in the stein. The mount shown in Fig. 1 comprises a fiat 'plate-'like electrode I1, preferably a sheet of metal bent at the edges as illustrated and secured to a pair of the supports I6; a grid-like electrode I8 made, like the usual grid, of tranverse grid wires secured to two parallel side rods; and aiilamentary cathode of the usual M shape, and consisting of two loops I9 mounted in the same plane and electrically connected in parallel. These three electrodes are substantially flat and are mounted side by side in parallel planes, as in the usual fiat type of three electrode fllametary cathode tubes. The three electrodes are rigidly spaced by an insulating spacer, such as a glass bead spacer 20 having projecting studs 2i secured to `the upper ends of the plate supports and of the side rods of the grid-like electrode I8 and also having two filament hooks 22 for holding the bights of the filament loops in position. The filament may be approximately of the dimensions of the filamentary cathodes used in commercial tubes, and a suitable filament drop in each of the loops is, for example, about 31/2 volts.

In accordance with my invention I mount behind the cathode on the side opposite the gridllike electrode I8 an auxiliary or backing electrode,

such as a plate-like electrode 23, which may conveniently be made of sheet metal bent up at the edges to form flanges 24 which, as shown in Figs. `1 and 2, extend inside the edges of the electrode I1. This auxiliary electrode may be mounted on a pair'of the supports I6, as shown in Fig. 1. The grid-like electrode I8 is substantially the usual grid with one side removed, and the external electrode I1 is substantially half of the at or box type plate electrode commonly used in commercial tubes. structurally the tube resembles the usual flat type three electrode tube having a nlamentary M shaped cathode, with the grid and plate at one side or in front of the cathode, and, in addition, an auxiliary electrode or backing plate 23 coextensive withand behind the fllamentary cathode, and in a plane parallel to the plane of the cathode.

When the tube shown in Fig. 1 is connected in a Barkhausen-Kurz oscillation circuit, as shown in Fig. 6, the grid electrode I8 is at a high- 1y positive potential and becomes Ithe anode, and the electrode I1 in front of the anode is at a lower positive or even somewhat negative potential, so that it acts primarily as a limiting electrode to produce parallel to said cathode and anode an equipotential region ,of substantially the same potential as said cathode for limiting the extent of travel of the electrons through the grid-like highly positive anode I1. The term potential is used in this application in the usual sense and means potential with reference to `the cathode, which is consideredI a point of zero potential and with reference to which the other electrodes may be positive or negative. I! the backing electrode I'I were absent, the tube would not voperate as a Barkhausen-Kurz oscillator-.possibly because the potential in the region or space adjacent and in the plane oi' the cathode. and particularly in the space between the sides of the loops I9 of the cathode, is positive, since the potential of this space is the resultant of the effects of the cathode and of the highly positive lgrid-lilre-anode Il.

In accordance with my invention I have provided means, such as the negative auxiliary or backing electrode 23 behind the cathode by which this positive potential of the region in the plane of the cathode, and especially of the space between the sides of the loops of the iilamentary cathode, may be counteracted to any desired extent. The auxiliary electrode may be made sufficiently negative to lower this space potential to the point where the tube will produce high frequency oscillations. I have found that when associated with suitable circuits a tube constructed as shown in Fig. 1 will produce relatively strong ultra high frequency oscillations. The tube may conveniently be made with an M shaped thorited tungsten filament activated to have high emission and consisting o f the two V shaped loops I9 connected in parallel each loop4 being about 5 mm. wide at the open end, and having a filament drop of about 3% volts and a filament current of about 1.25 amperes. The anode I! may be made like a grid of 5 mil grid wire with 35 wires per inch. The electrode spacing may be about 1 mm. between the auxiliary electrode 23 and thel cathode; 1.5 mm. between cathode and anode I8; and 1.5 mm. between the anode and the limiting electrode I1. Such a tube may be operated with the grid-like anode IB at about 250 volts positive, the limiting electrode I1 somewhere near zero potential, and the auxiliary or backing electrode 23 at from 5 to 20 volts negatential surface in the plane of the nlamentary cathode. Such an equi-potential surface may, in conjunction with the electrodes, cause the time of travel of the electrons to be about the same on each side of the grid electrode, and hence cause the conditions in the tube to be favorable Yfor the development of ultra high frequency oscillations. f

The spacing of the grid-like anode and the cathode with spaced sections should be either approximately the same, or less than the .interspacing of the cathode sections. In the particular tube shown in Fig. 1 the interspacing of the filamentary sections is the average distance between the sides of the V shaped loopof the filament. iting or fronting electrode should be substantially equal to or greater than the spacing of the anode and the cathode. The spacing of the auxiliary or backing electrode and the cathode depends to some extent on the negative voltage applied to The spacing of the anode andthe limby side in a plane coaxial aoaaaea the auxiliary electrode, and is not particularly Critil.

By my invention it is feasible to ineke an ultra high frequency tube of the fiat type with a single straight cathode. or with a iilamentary cath-` ode having its sides or electron emitting portions spaced quite i'ar apart. As a result of my invention some serious limitations which have heretofore hampered the design and limited the output of vacuum tubes for producing high frequency oscillations are greatly lessened. For example. in tubes used for producing Barkhausen-Kurz oscillations the grid-like anode operates at high potential, and may reach a brilliant'white heat due to electron bombardment. When the cylindrical type of tube is used for generating these oscillations the cathode emission is a rather critical factor, and since the grid-like anode is very close to the cathode, the heat radiated from a very hot grid-like anode may affect the temperature and seriously modify "the emission of the cathode, particularly of a` high emission low temperature cathode, such as a.thoriated tungsten `illarnent or oxide coated cathode which normally operates at a dull red heat and is relatively sensitive to temperature. In` a tube embodying my invention such low temperature cathodes may be used, as vI have found that in my tube the cathode emission is not critical and may be varied between wide limits without adversely affecting the operation of the tube. Other general advantages are obtained because the anode may be designed to have good radiation and to operate at a comparatively low temperature.

The auxiliary or backing electrode 23 need not be in the form of a plate or sheet of metal. nor need it be fiat. It may, as shown in Fig. 3, b e curved, or otherwise shaped so'that the potential in the plane of the filament will approximate' an equipotential surface at a somewhat lower negative potential on the auxiliary electrode than is required when the auxiliary electrode is iiat.

One advantageous shape is that shown in Fig. 3,

where the auxiliary electrode has on its surface and in registry with the interspaces between the adjacent electron emitting sections of the cathode projections 25 which come closer to the plane of the filament than the other parts of the electrode surface which are in registry with vthe cathde sections themselves. a

Fig. 4 is an embodiment of my invention in a tube having a straight cathode associated 'with a coplanar auxiliary electrode. In this tube the limiting electrode 26 is made like the plate electrode and the perforated anode 21 is made like the grid of the commercial tubes having the fiat type of mount. -The cathode may have one or more straight electron emitting sections, and in this particular tube consists of two straight electron emitting sections or filaments 28,` positioned side with the electrodes 26 and 21, and shown connected in parallel, although they may be connected in series if desired. These filaments 28 are secured at their lower ends to a pair' of the supports i6, and Supplied wi'th current by one of the supports, and at the upper ends are connected by a conductive jumper 23.4 A current 'supply lead `,ill isl connected through a flexible connector to the upper end i ments. 'Ihe filaments are supported at their upper ends by resilient filament supports 3l projecting from a bead spacer 32, which also spaces the other electrodes by meansof projecting studs 3'3.

i The auxiliary electrode is closeto and preferably `and the auxiliary electrode are coplanar and pov45, connected tothe of one ofthe filaf in the same plane as the cathode so as to affect the potential of the space adjacent the cathode. In the tube shown the auxiliary electrode ccnsists of'three dat strips 34, mounted coplanar with the filaments 2l and connected at their up- 5 per end bya conductive jumper, and held in position by a pair of the supports i6 and by the bead spacer 32. t

In this particular form of tube the filaments 23 sitioned coaxial of the electrodes 26 and 21, so that the mount of the tube is symmetrical. The potential of the region on each side of each filament 28 can be affected by the potential applied to the adjacent strips 34. As the edges of the l5 strips are quite close to the filaments, each filament has a strip of the auxiliary electrode on each side and close to it, and is in effect in a slot in the auxiliary electrode.

I have found that a tube constructed as shown in Fig. 4 with'straight filaments 28, each having i a filament drop of' about 3 volts, and connected in circuit as shown in Fig. 9, will produce ultra high frequency oscillations with a positive potential of about 250 volts on the electrode 21, and a potential on the auxiliary electrode strps 34 oi' about 2 volts positive, which is approximately the mean or vaverage potential of the filaments. Under these tube of Fig. l may be used to generate high fre- 35' quency oscillations.

In'Fig. '7 the tuned output circuit of the generator is shown as,.a Lecher system tuning circuit connected to the grid-like anode i8 and the limiting electrode I1, and hav- 4 ing two parallel wires 39 and 40 bridged by a 4i) movable bridge 4I in which is a'blocking condenser 42. The anode wire 39 and the limiting electrode Wire 40 of' the Lecher system are rconnected through inductances 43 to the battery 44 and to the cathode I9 output circuit need not be connected exactly as shown, as it may be associated with the tube in other ways and with other electrodes of the tube.v as is well understood in the art. Other types of resonant for tuned output circuits may also be used. Y y

- Fig. 7 is a diagram of al circuit for using the tube of Fig. l as a modulator. The circuit is much the same asin Fig. 6, but with the inductances 43. placed at the ends of thebridge 4I, and an 55 input circuit, comprising anl input"'transfonner auxiliary electrode 23. Fig; 8 is a diagram of the tube of Fig. 4 .connected ina 'cn-cuit similar -to Fig. 6. with a positive potential of 250 'volts on the anode, and 60 'a positive potentialof 2 to 21/2 volts on the auxiliary electrode 34, ultral high` frequency oscillationsare generated and appear in the output circuit. 4

.While I have shown and described a preferred embodiment of my invention, I do not wish to be limited to this particular form, as devices constructedin accordance with the principles of my invention may be made in various forms and modifications without departing from the scopef set forth inthe appended tron discharge tube having a thermionic cathode respectively. This tuned Rif" 4 I 2,022,9sa

with spaced electron emitting sections mounted side by side in the same. plane, a perforated an- 'ode parallel to the plane of said cathode, a limiting electrode in front of said anode opposite said cathode and spaced from said anode a distance at least equal to the spacing between said anode and said cathode, a backing conductor parallel to and in operative. juxtaposition to the electron emitting sections of said cathode, a source of potential with reference to said cathode for impressing a high positive potential on said anode, a potential approximately that of said cathode on said limiting electrode, and on said backing conductor a potential which makes the space potential between the parallel sections of said cathode substantially the same as the potential of said sections, and a tuned output circuit including said anode.

2. An oscillation generator comprising an electron discharge tube having a perforated electrode and an auxiliary electrode presenting parallel surfaces,y an electron emitting electrode between said other electrodes and comprising a plurality of parallel iilamentary sections positioned in asurface parallel to said other electrode surfaces and spaced apart a distance at least approximately :as great as' the distance between said sections and said perforated electrode, a limiting electrode on the side of said perfor'ated electrode .opposite said cathode and presenting a surface parallel to said other electrodes, and a source of potential with reference to said electron-emitting electrode for impressing on said perforated electrode a high positive potential, on said limiting electrode a potential approximately that of said cathode, and on said auxiliary electrode a potential sufficiently negative to make the space potential in the plane of said electron emitting electrode and between said electron emitting sections approximately the same as the potential of said sections, and a tuned output circuit including said perforated.

electrode and another electrode of said tube.

3. An oscillation generator comprising an electron discharge tube having a 'fllamentary thermionic cathode with spaced electron emitting sections side by side in the same plane, al perforated fiat anode in front of said cathode and parallel to the plane oi' said cathode, a cold fiat limiting electrode in front of and parallel to said perforated anode and spaced from it sub-.- stantially the same distance as between said Aanode and said cathode, a cold flat auxiliary electrode behind and coextensive with said cathode and parallel to the plane of said cathode, a

y tuned output circuit including said anode, and

a source of potential with reference' to said cathode for impressing a high positive potential on said anode, a negative potential ony said auxiliary electrode to substantially neutralize the field of `said anode in the spaces between said cathodev sections, and substantially zero potential on said limiting electrode.

4. An oscillation generator comprising an electron discharge tube having a perforated anode, a cold nat front electrode in front -of and parallel to said anode, a thermionic cathode with spaced electron emitting sections mounted side by side behind said anode in a plane parallel to said perforated anode and spaced from said front electrode a distance substantially the same as and from said anode a, distance no greater than the spacing between said cathode sections, a cold fiat backing electrode parallel to said front electrode and behind and overlapping said cath- 5. An oscillation generator comprising' iin-l0V electron discharge tube having a tbermionic cathode withspaced electron emitting sectionsn mounted side by side in the same plane, a perforated anode parallel to the plane of said cathode, a limiting electrode external of and parl5' allel to said anode, a backing electrode positioned Y to make the potential to the anode of said seci tions of the cathode and of the interspaee between said sectionslin the plane of said cathode approximately the same', a source of potential 20 with reference to the cathode for maintaining said perforated anode at a positive potential. said limiting electrode at substantially zero potential, and said backing electrode at a negative potential and a tuned output circuit including said anode and one of said other electrodes.

6. An oscillation generator comprising an electron discharge tube having a perforated anode, a thermionic cathode with spaced electron emitting sections mounted side by side in a plane parallel to said perforated anode Vand spaced from said anode a distance approximately no greater than the spacing between said sections. a limiting electrode mounted external of and parallelto said anode, an auxiliary electrode adjacent said cathode and on the side of said cathode opposite said anode, a source of potential with refex'ence to said cathode connected to maintain said anode at a positive potential, said Hunting electrode at a potential lower than that of said anode, and said auxiliary electrode at a negative potential, an input circuit connected to said auxiliary electrode and said cathode, and an output circuit including said anode and said limiting electrode. y 7. An oscillation generator comprising an electron discharge tube comprising a iiat perforated anode, a straight cathode in a plane parallel to said anode, an auxiliary electrode coplanar with said cathode and comprising two iiat strips on,.' 0 opposite sides of said cathode with their edges adjacent said cathode, a limiting electrode parallel to and on the side of said anode opposite said cathode, a source of potential with reference to saidcathode for impressing a high positive "potential on said anode, substantially zero potential on said limiting electrode, and a low positive potential on said auxiliary electrodeand a tuned output circuit connected to said anode and said auxiliary electrode to respond to electron oscillations between said cathode and said anode.

8. An oscillation generator comprising an electron discharge tube having a thermionic cathode with spaced electron emitting sections mounted side by'side, a perforated anode parallel to the plane of said cathode, an auxiliary electrode coplanar with said electron emitting sections, a limiting electrode parallel and on the side ofl said anode opposite said cathode, a source of potential with reference to` said cathode for impressing a high positive potential on said anode. substantially zero potential on said limiting electrode, and a potential substantially the average potential of said cathode sections on said auxiliary 15 electrode, and a tuned output circuit including said cathode.

9. An oscillation generator'comprislng an electron discharge tube having a thermionic cathode comprising two straight laments mounted side by side and connected in parallel, a perforated anode parallel to the plane of said cathode, an auxiliary electrode comprising a metal strip coplanar with said filaments and with its edges ad- 10 jacent said iilaments, a limiting electrode parallel to and on the side of said anode opposite said cathode, a source of potential with reference to said cathode for impressing a high positive potential on said anode, substantially zero potential on said limiting electrode and a low positive potential approximately the average positive potential of said cathode sections on said auxiliary electrode, and atuned output circuit including said cathode. 

